How much more can they really do at this point?
I mean, the content is there to be tested as is, otherwise it wouldn't be there.
It's not like what we see now is going to be completely different from when the beta comes out, or when the expansion goes live.
Alpha/Beta testing is testing the intention of the content being designed. It's not, "this is one way we plan to do things, but we have a bunch of other options we plan to roll out". It's, "this is what we're really aiming for, but we're open to feedback about it."
"Feedback" is not going to cause any major reworking of features that are already rolled out and being tested on the alpha. That's what they should have been doing when they were at the drawing board for Legion. What you see now is pretty much the basis for what you're going to get.
If the alpha testers feel that the Order Halls missions are too similar to Garrisons, then I would imagine that they're intended to be that way. Otherwise, the initial first-draft version would have been anything but that.